Typically, a wafer board panel comprises layers of wood flakes or wafers formed into a composite structure using a resinous binder. The preparation of wafer board panels is complex, but broadly consists of two principal stages. The first stage comprises the preparation of the wafers and the admixing thereof to form a loose layer or mat; the second stage involves subsequent compression and heating of the mat to cure the resin and form the consolidated panel.
Until recently, wafer board was manufactured in the form of planar or flat sheets. However, as disclosed in U.S. Pat. No. 4,616,991, the present applicant has developed an apparatus and process for the manufacture of panels having a wave-like or corrugated configuration. Such wave-board panels have improved structural strength properties, relative to planar panels.
This prior patented apparatus involved a pair of opposed, spaced-apart, upper and lower platens. Each platen was formed of adjacent lengths of chain-like links. When the lengths were pushed inwardly from the side, they would shift from a planar to an undulating corrugated form.
The process steps involved:
distributing a mat of loose wood wafers between the upper and lower platen surfaces while they are maintained in the planar configuration; PA0 biasing the platens together to pre-compress the mat, and thereby substantially fixing the wafers together to limit their further relative movement; PA0 converting the two platen surfaces, still in pressing association with the mat, from the planar to the corrugated configuration; and PA0 then applying additional pressure and heat for a sufficient time to cure the binder and produce a corrugated wave-board panel.
The main advantage inherent in the patented process was that the panel product so formed was characterized by having a substantially uniform density. This was achieved because the wafers were fixed by the pre-compression step and because the mat was not significantly stretched or elongated during the conversion from the planar to the corrugated configuration.
It will be also noted that the panel product formed using the particular mechanical assembly described hereabove is limited to a sinusoidal configuration. The peaks and troughs of the panel have a generally rounded profile.
Certain applications of corrugated wave-board may involve the attachment of a corrugated wave-board web to either a single or two planar stressed-skin panels. Usually, the separate pieces are secured together by means of adhesives or by fastening elements. However, because of the limited contact area between the rounded peaks and troughs of the wave-board and the adjacent skins, it is often difficult to secure the separate pieces together with any stability.
In order to overcome this limitation, applicants contemplated the provision of a wave-board characterized by a flat-topped (or flat-peaked) and a flat-bottomed (or flat-troughed) profile. This change would increase the available attachment area between components and thus provide improved stability. Starting from this concept a particularly configured wave-board and a press platen assembly for manufacturing the wave-board has been developed.
Turning now to prior art patents. Nishibori, in U.S. Pat. No. 4,610,900 teaches a wood-like molded product of synthetic resin prepared by mixing a synthetic thermoplastic resin with a fine aggregate of cellulose base. The resin comprises the bulk of the product rather than the cellulose. The product is then subjected to a sanding or jetting treatment on its surface hardened layer.